Trunk-circuit for telephone systems.



No. 848,749. PATENTED APR 2., 1-907.

J. B. KELLEY & E. B. HEAFORD.

TRUNK CIRCUIT FOR TELEPHONE SYSTEMS. APPLICATION II'LED DEC. 31, 1906.

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N0r 848,749. PATEN'IED APR. 2, 1907- I B. KELLEY B. HEAFORD. I TRUNK CIRCUIT FOR TELEPHONE SYSTEMS.

APPLICATION FILED 1020.31, 1906.

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irnrrnn STATES EAEENT orrIoE.

JOSEPH BERYL KELLEY AND EDWIN BOWEN HEAFORD, OF OMAHA,

NEBRASKA.

TRUNK-CIRCUIT FOR TELEPHONE SYSTEMS.

Specification of Letters Patent.

Fatented April 2, 1907.

Application filed December 31, 1906. fierial No. 350,302.

To ctZZ w/wm it may concern:

Be it known that we, JOSEPH BERYL KEL- LEY and EDWIN BOWEN HnAFoRD, citizens of the United States, residing at Omaha, in the county of Douglas and State of Nebraska, have invented a new and useful Trunk-Circuit for Telephone Systems, of which the following is a specification.

This invention relates to telephone systems of the common-b attery multiple-switchboard type, and relates more particularly to an automatic trunk-circuit by which any local station or exchange in the system can signal to a toll operator by means of the usual battery in the cord-circuit of such exchange or local station, the two sides of the talking or trunk circuit being employed, so that a third wire is rendered unnecessary. A two-wire automatic trunk-circuit of this character is adapted for use in connection with the cords of a common-battery exchange connected to the trunk-circuit and with toll-cords having suitable resistance or retardation bridged across their tip and sleeve wires-as, for instance, in connecting the local subscribers with the toll-board or office. i

The invention hasfor one of its objects to provide a signaling system which is thoroughly reliable and efficient in use and of extremely simple arrangement.

A further object is the provision of a trunkcircuit having a toll-board signal controlled by a relay bridged across the two sides of the trunk-circuit and arranged to be actuated by current received from the battery at the central-exchange switchboard.

Another object is the employment of a lock-out circuit used in connection with the signaling device, so that the signal cannot again be actuated until the exchange operator has removed the cord-plug, whereupon the signaling apparatus is restored to normal position and is capable of being again actuated by the insertion of the cord-plug.

With these objects in view and others, as will appear as the nature of the invention is better understood, the invention comprises the various novel features of construction and arrangement of parts, which will be more fully described hereinafter and set forth with particularity in the claims appended hereto.

In the accompanying drawings, which illustrate one of the embodiments of the invention, Figure 1 is a diagrammatic view of the trunk-circuit with the various apparatus therein in normal position. Fig. 2 is a similar view showing the call-plug of the ex change cord-circuit inserted in the trunkjack and showing the toll-signal circuit com pleted. Fig. 3 is a diagrammatic view of the trunk-circuit connected with the central-exchange switchboard and toll-switchboard of another station, the signal circuit being looked open.

Corresponding parts in the several figures are indicated throughout by similar characters of reference.

In the present instance we have elected to illustrate only the trunk-circuit and the necessary apparatus therein in connection with the calling and answering plugs of the cordcircuits at the exchange and toll switchboards, it being understood that the cordcircuits will be of any suitable arrangement.

Referring to the drawings, A designates generally the trunk-circuit, B the local switchboard or exchange station, and C the toll-station, the calling and answering plugs of the cordcircuits of the said stations being shown as suficient'to enable a proper understanding of the invention.

The trunk-circuit consists of two wires 1 and 2, terminating, respectively, at the tipsprings 3 and sleeve-springs 4 of the jacks at the central exchange or local board B and toll-switchboard C. The'cordcircuit plugs 5 and-6 are of the usual form, and when the cord-circuit of the station B is of the threewire type the thimble 7 is grounded through a suitable resistance 8.

Bridged across the conductors 1 and 2 of the trunk at a point adjacent the toll-switchboard is a relay 9, having a coil 10 of high resistancesuch as twelve thousand ohms, for instancewhich is connected by-the wires 11 and 12 to the two sides of the trunk-circuit. This relay is provided with a ground ed armature 13 for controlling the tolloperators signal. In the present instance a lampsignal 14 is employed which is connected with the positive side of the exchange-battery 15 and through the wire 16 and armature 13 to ground at 17. The line-lamp 14 is cut out of service at the proper time by the relay 17, having its coil connected in the sleeve side 2 of the trunk-circuit, said relay actuating the armature 18, that is included in the conductor 16 on the grounded side of the signal-lamp. The relay 17 is of a resistance of about seventy to eighty ohms, and shunted around the same is a non-inductive winding or equivalent means, (indicated at 19.) On the relay 17 is wound a cut-out coil 20 of about thirty ohms, which is connected with the positive side of the exchange-battery 15 and is adapted to make contact with the armature 18, so that current will pass from the battery 15 through the wire 21, coil 20, armature 18, conductor 16, armature 13 to ground 17, while the bridged relay 9 is energized so that the signal-lamp will be positively locked out.

On the tip side 1 of the trunk-circuit A is arranged the relay 22, connected in series with the conductor 1 and provided with an armature 23, which when actuated serves to bridge across the conductors 1 and 2 the relatively low-resistance or retardation coil 24. The relay 22 is provided with the noninductive resistance-shunt 25 or equivalent means, for facilitating the passage of the voice-currents. In series with the exchangebattery 15 and lock-out coil 20 is a resistancecoil 26 of about thirty-ohms value, and this non-inductive resistance serves to prevent excessive battery-currents through the sec- 0nd or lock-out coil of the relay 17 when the bridged relay 9 is denergized, and thus in sure the releasing of the armature 18 and obviate possible sticking thereof.

When a subscriber signals the exchange operator for a connection with the toll-station, the operator places the plug 5 in the jack at the switchboard B, so that the circuit from the battery of the exchange is completed through the wires 2 11, relay 9, and wires 12 and 1, as will be readily understood by reference to Fig. 2. Owing to the high resistance of the relay 9, the value of the current is such that the supervisory lamp in the exchange cord-circuit is not lighted. The relay is thus energized by the insertion of the call-plug in the switch-jack at B, so that the armature 13 closes the signal-lamp circuit, thereby causing the lamp to light and inform the toll operator. Upon inserting the answering-plug 6 the toll operator causes the bridged resistance or retardation coil 27 of the cord-circuit 28 to complete the batterycircuit from the exchange B through the two sides of the trunk-circuit and coils of the relays 17 and 22, so that the armatures 18 and 23 are moved to the positions shown in Fig. 8. The energizing of the relay 17 causes its armature 18 to interrupt the lamp-circuit and connect the cut-out coil 20 through the said armature 18, conductor 16, armature 13, to ground at 17. Current now flows from the battery 15 through this grounded path, so that the armature 18 will be positively held out of the signal-lamp circuit as long as the exchange operator leaves her plug in the jack at the switchboard B, it being understood that the relay 9 is thus maintained energized. The signal-lamp will be locked out of service during conversation through the system and even after the toll operator withdraws the plug 6 from the jack of the switchboard C, and the lamp-circuit is only returned to normal position by the exchange operator withdrawing the plug 5 thereby breaking the circuit that energizes the relay 9, so that the armature 13 can return to the position shown in Fig. 1. The energizing of the relay 22 causes the retardation-coil 24 to be cut into circuit across the lines of the trunk, so that the supervisory signal at the exchange B will be operated should the resistance 27, connected across the toll cord-circuit in series with the line,be too great to accomplish this.

From the foregoing description, taken in connection with the accompanying drawings,

the advantages of the arrangement of the various apparatus and of the method of operation will be readily apparent to those skilled in the art to which the invention appertains, and while we have described the principle of operation of the invention, together with the apparatus which we now consider to be the best embodiment thereof, we desire to have it understood that the apparatus shown is merely illustrative and that various changes may be made when desired as are within the scope of the claims.

What is claimed is 1. In a telephone system, the combination of an exchange-station, and a toll-station, with a two-conductor trunk-line, a signal-circuit associated with the trunk-line, a bridged relay for closing the signal-circuit when the exchange-station is connected with the trunkline, a relay for opening the signal-circuit when the toll-station is connected with the trunk-line, and a means for looking out the signal as long as the bridged relay is energized.

2. In a telephone system, the combination of an exchange-station, and a toll-station, with a two-conductor trunloline, a signal, a battery connected therewith, a signal-circuit, a relay bridged across the trunk-line and having a grounded armature adapted to close the signal-circuit when the exchange-station is connected with the trunk-line, a relay in the trunk-line energized when the toll-station is connected with the trunk-line and having an armature for opening the signal-circuit, and a lock-out means supplied withcurrent from the said battery for holding the signal-circuit open as long as the bridged relay is energized.

3. In a telephone system, the combination of an exchange-station, and a toll-station, with a two-conductor trunk-line, a signalcircuit including a source of current, a relay of high resistance bridged across the trunkline to be energized by current from the ex- IIO change-station When the latter is connected With the trunk-line and provided With a grounded armature adapted to close the signal-circuit, a relay-coil in series With one side of the trunk-line and having an armature for opening the signal-circuit When the toll-station is connected With the trunk-line, and a lock-out coil connected With the source of current in the signal-circuit and connected with ,the armature of the series relay when the latter is actuated and grounded through said armature and the armature of the bridged relay for holding the lamp-circuit open as long as the bridged relay is energized.

4. In a telephone system, the combination of an exchange-station, and a toll-station, With a two-conductor trunk-line, a signalcircuit including a battery having one side grounded, a relay bridged across the trunkline and having a'grounded armature for closing the signal-circuit, a cut-out relay in one side of the trunk-line and provided With an armature included in the signal-circuit for opening the latter, and means dependent upon the bridged relay for holding the armature of the cut-out relay in open circuit.

5. In a telephone system, the combination of an exchange-station, and a tolLstation, With a two-conductor trunk-line, a signalcircuit including a battery having one side grounded, a relay bridged across the trunkline and having a grounded armature for closing the signal-circuit, a cut-out relay in one side of the trunk-line and provided With an armature included in the signal-circuit for opening the latter, a lock-out coil on the latter relay adapted to be connected With the armature of the cut-out relay When the latter is actuated, and a resistance-containing conductor connected With the ungrounded side of the said battery and With the look-out coil.

6. In a telephone system, the combination of an exchange-station, and a toll-station, With a two-conductor trunk-line, a signalcircuit including a battery having one side grounded, a relay bridged across the trunkline and having a grounded armature for closing the signal-circuit, a relay connected in series With one side of the trunk-line and provided With an armature included in the signal-circuit for opening the latter, a lock out coil on the last-mentioned relay adapted to be connected With the armature of the same When the latter is actuated, a resistance-containing conductor connecting the lock-out coil With the ungrounded side of the said battery, a relay-coil connected in series With the other side of the trunk-line, and a conductor containing retardation bridged across the trunk-line by the armature of the last-mentioned relay.

In testimony that We claim the foregoing as our own We have hereto affixed our signatures in the presence of two Witnesses.

JOSEPH BERYL KELLEY. EDWIN BOWEN HEAFORD -Witnesses:

WV. P. BoWLER, JOHN ALBERT. 

